1. Field of the Invention
The present invention relates to the field of three-way poppet valves.
2. Prior Art
An object of the preferred embodiment of the present invention is to have a high pressure (for fuel) three-way valve with low leakage, good pressure balance (for minimal force requirements) and practical manufacturing. While the valve of the present invention has other uses, the preferred embodiment is intended for use in fuel injector for fuel injected engines, and the prior art will be discussed primarily with respect to such use.
“Conventional” two-way needle control valves to control the motion of a diesel injector's needle valve have been in use for quite some years. They provide acceptable but not superior controllability with relatively low cost. On the other hand, needle control with three-way valves has not been commercialized to the same extent. Three-way control valves provide superior flexibility in controlling the needle motion but are difficult to manufacture and/or to achieve pressure balance.
It is a very simple task to achieve pressure balance with a two-way valve but more difficult with a three-way valve. It is also simple to achieve pressure balance with three-way valves if a spool valve is used, but a spool valve leaks excessively if used with fuel at elevated pressures as required for fuel injected engines. Therefore most needle valve control is achieved by using a two-way poppet valve.
Direct needle control with two-way valves is relatively simple and low cost. However, the flexibility in controlling the needle motion during both opening and closing through the entire pressure range is not optimal, since there is no specific orifice to control the opening rate and closing rate independently, as is the case with a three-way valve.
U.S. Pat. Nos. 5,463,996, 5,673,669 and 5,697,342 show three-way poppet valves used in fuel injectors, with the valves using the valve element to center the second seat. However, none of the valves are able to achieve the pressure balance of the present invention.